High Speed Packet Access (HSPA) is a technology used for data traffic in mobile communication systems. With HSPA it is now become possible to provide mobile broadband services since the peak bit rates reach up to 42 Mbps in Third Generation Partnership Project Release 8 (3GPP R8) for the downlink, and 11 Mbps (3GPP R8) in the uplink. For 3GPP R9 the peak rates are doubled. Bit rates of this magnitude are sufficient for many applications and can provide good user experience. However, these figures only represent part of what the user will experience when using these systems.
A common traffic type for internet connections is so-called bursty traffic, i.e. traffic having very high peak loads interrupted by periods with low or now load. Bursty traffic is for example common for many types of WWW sessions and uploads of small files. In these situations the user will never reach the above mentioned bitrates because in many situations rather slow ramp up period of the user's bit rate, i.e. user's Transport format is slowly increased. The reason for having a rather restrictive transport format ramp up is to ensure the system stability. If a too fast transport format ramp up, possibly from more than one user simultaneously, may create a high noise rise peak, which in turn will have a negative impact on coverage and capacity.
In existing HSPA systems noise rise is the limiting resource in the uplink. The system strives to utilize as much as possible of the allowable noise rise by increasing the Transport Format Combination (TFC) which in turn limits the maximum bit rate a UE can utilize for the active users in a controlled matter until it reaches the noise rise limit. If the noise rise limit is exceeded, the system will decrease the TFCs depending on how severe the noise rise peak is.
There is a constant need to improve the performance in mobile communication system. Hence, there exists a need for improving transmission of data traffic in a mobile communication system.